The present invention relates generally to the field of electronic security systems and, more particularly, to a cost effective keypad entry system which provides high levels of security, convenience and flexibility in operation.
Individual push-button operated locks have been used to secure doors of dwellings and vehicles. Such locks are described in U.S. Pat. Nos. 3,953,769, 4,149,212, and 4,477,806, each of which discloses a stand-alone push-button lock which is programmed at the lock itself to open in response to an access code.
The only push-button or keypad operated system known to applicant for securing a large number of doors was manufactured by Tool Research Engineering of Santa Ana, California, under the name "Digikey". The Digikey system has a "dummy" keypad without local storage or processing capabilities at each guest door of a hotel. The keypads are connected together as an operating unit by a large number of wires leading to a front desk computer.
In the Digikey system, a four-digit number entered on a room keypad is transmitted to the front desk computer which makes the decision as to whether the number is a valid access code. If the number is valid, a signal from the processing unit unlocks the door. The valid access code for a room is chosen by the guest when he checks in to the hotel. To do so, he enters a four-digit number onto a keypad at the front desk. The number is then stored in the front desk computer for use in opening the door. As far as applicant is aware, there is no provision in the Digikey system for deviating from a four-digit entry code, and only one code can be stored for each room.
Other systems for controlling access through doors of a large building complex use machine-readable "card keys" which may or may not resemble mechanical keys. Such devices are described in U.S. Pat. Nos. 3,622,991; 3,694,810; 4,157,534; and 4,415,893. Of course, the use of physical keys of any type carries with it one of the basic disadvantages of traditional mechanical locks, i.e., that the number of possible key variations is only as great as the number of keys used. While some of the physical key systems listed above have storage and comparison capabilities at each door to be opened, many of them are cumbersome in their implementation. For example, the devices of U.S. Pat. Nos. 3,622,991 and 4,157,534 require extensive hardwire networks or microwave transmission devices for communication. Complex hardwire networks are unsuitable for large installations and are difficult to install in existing buildings. U.S. Pat. No. 4,415,893 is unique in that it repeatedly states that it is desirable to retain the mechanical parts of a conventional door lock, with the pin tumbler replaced by an electronic reading cylinder of identical size. This is proposed for the purpose of maintaining the "feel" of a mechanical lock and clearly teaches away from development of a sophisticated keyless system.
Therefore it is desirable in many applications to provide a highly secure system for controlling and monitoring the opening of a large number of doors in a cost-effective manner.